1. Field of the Invention
This invention relates to an electronic communication system. In particular, this invention relates to a method and an apparatus which provide the features of the commonly known Registered Mail in an electronic communication system.
2. Description of the Prior Art
In a presently known electronic communication system (see, for instance, article "A Prototype for the Automatic Office" by Robert B. White, Datamation, April 1977, pp. 83-90) messages are edited, then sent from a sender and finally received by the mailbox of a receiver. There may be a large number of receivers, and receiving is, for instance, according to a distribution list. To a certain extent, the presently known electronic mail systems of this type can replace the conventional paper mail system effectively.
Also simple security features such as secrecy features have been conceived for communication systems. For instance, symmetrical key systems, such as the well-known DES (Data Encryption Standard, see National Bureau of Standards, Federal Information Standard FIPS Publication 46, U.S. Department of Commerce, Washington, D.C.; January 1977) have been used in conjunction with electronic communication systems. However, these security features are relatively simple. Especially a security method and a security system providing the same features and advantages as the conventional Registered Mail System have not yet been suggested in connection with fully electronic digital communication systems. When the transmission of a message from a sender A to a receiver B is considered, the conventional paper/envelope Registered Mail System in most Postal Services provides the following features:
(a) The receiver B must sign a receipt before he can receive a message. The receipt is returned to the sender A.
(b) The sender A is not able to change the message for which he has obtained the receipt from the receiver B.
(c) The receiver B is neither able to successfully fully disclaim having received a message after he has signed the receipt, nor to change the message.
(d) In some mail system there is a procedure which can be referred to as a "time stamp mechanism". In the course of this procedure, the point of time of the transaction, in particular of the releasing of the letter to the receiver, is marked. Thus, the time of the transaction is traceable by a third party, for instance, in court, when the transaction is disputed.
An electronic Registered Mail System should have the above-mentioned features (a), (b) and (c). It preferably should also have the feature (d).